Radiation has been employed to image and treat tumorous tissue. In radiation therapy, a high energy beam is applied from an external source towards the patient. The external source, which may be rotating (as in the case for arc therapy), produces a collimated beam of radiation that is directed into the patient to the target site. The dose and placement of the dose must be accurately controlled to ensure that the tumor receives sufficient radiation, and that damage to the surrounding healthy tissue is minimized.
Sometimes, in a radiation treatment procedure, a plurality of treatment sessions may be performed. In each treatment session, a radiation source may be placed at a prescribed gantry angle to thereby deliver radiation beam towards a target tissue from a certain angle. As a result of delivering radiation towards the target tissue from a plurality of different angles, a sufficient radiation dose may be delivered to the target tissue to thereby treat the target tissue, while surrounding healthy tissue may be protected.
Patient movement during radiation delivery may significantly affect the outcome of the procedure. For example, in a radiation treatment procedure, patient movement affects dose distribution in patient. One method of controlling this phenomenon is to use gated treatment. In gated treatment, dose is only delivered while patient is in a position or phase (e.g., breathing phase) that is prescribed for radiation delivery. For example, in a treatment plan, the radiation may be prescribed to be delivered only when the patient is relatively stationary (e.g., when the patient is in full inhale or exhale positions) for some period of time, and when there are not any unnecessary critical organs that would receive radiation when a target in the patient is radiated.
In existing gated treatment methods, the treatment has been planned as one continuous delivery. The operation of the radiation machine is stopped to pause the continuous delivery when the patient is not in a planned phase or position. The operation of the radiation machine is resumed only when the patient is back in a planned phase or position. Therefore the time when patient is not in planned phase or position is lost in delivery efficiency sense.